This invention relates to a piezoelectric resonance tyeknock sensor to be rigidly connected to a cylinder or other component of an internal combusion engine to detect knocks that may occur in the cylinder of tile internal combustion engine.
A known resonance type knock sensor is illustrated in FIG. 1. The illustrated sensor typically comprises a vibration sensing member a realized by bonding an annular piezoelectric element b to a surface of a thin metal plate c as an integral part thereof and mounted by a supporting bolt d driven through the center of the thin metal plate on a case e to be fitted onto an internal combustion engine. The resonance frequency of the vibration sensing member needs to substantially agree with the vibration frequency of knocks to be detected. Japanese Patent KOKAI No. 58-218621 discloses a convenient method of making the two frequencies agree with each other, if they mutually differ, by arranging a pair of washers f and g coaxially on the opposite surfaces of the thin metal plate c and allowing the supporting bolt d running therethrough. With such an arrangement, since the thin metal plate c is pinched at the center by the washers f and g having a same diameter and the upper washer f needs to be placed within the through bore of the annular piezoelectric element b, the outer diameter of the washers f and g is inevitably made smaller than the inner diameter of the annular piezoelectric element b.
A piezoelectric resonance type knock sensor is, by definition, designed to detect vibration of an internal combustion engine given rise to by knocks, or knocking vibration as referred to hereinafter. Knocking vibration of the engine can be prevented or minimized by controlling the timng of igniting the fuel in the engine according to the information obtained by way of the knock sensor. Since a highly responsive sensor can transmit output signals with a high voltage level and hence at a favorable signal to noise ratio (S/N ratio), such a sensor will be effectively used in the operation of suppressing knocking vibration and improve the performance of a knocking vibration suppressing mechanism incorporating it. In other words, existing knock sensors need improvements in the responsiveness if a higher efficiency is to be achieved for suppressing knocking vibration in internal combustion engines. On the other hand, an improved knock sensor needs to be assembled without difficulty and allow an easy operation for electric connections.
It is, therefore, an object of the present invention to provide a piezoelectric resonance type knock sensor for an internal combustion engine that meets the above identified requirements.